Compressor

ABSTRACT

A centrifugal compressor system has a compressor housing partitioned into a plurality of chambers and a gear chamber that has a common wall with the compressor housing. A compressor module support structure is mounted in each chamber on the common wall and receives a compressor module that has a pinion gear that extends past the common wall for engagement with a bull gear mounted for rotation in the gear chamber. Each compressor module has an inlet shroud that is supported on an intermediate partition of the compressor housing and a large plenum chamber is defined in front of each compressor module in part by that intermediate partition.

United States Patent Heitmann et al.

[54] COMPRESSOR [72] inventors: Arnold M. l'leltmann, Swampscott; Robert0. Chambers, Medford, both of Mass.

Northern Research and Engineerlng Corporation, Cambridge, Mass.

(22] Filed: June8, 1970 [21] Appl.No.: 44,131

[73] Assignee:

[56] References Cited UNITED STATES PATENTS 3,355,097 11/1967l-lornschuch ..415/l79 Perrott ..417/243 Ford ..4l7/243 PrimaryExaminer-C. .I. l-lusar Attorney-Willis M. Ertman ABSTRACT A centrifugalcompressor system has a compressor housing partitioned into a pluralityof chambers and a gear chamber that has a common wall with thecompressor housing. A compressor module support structure is mounted ineach chamber on the common wall and receives a compressor module thathas a pinion gear that extends past the'common wall for engagement witha bull gear mounted for rotation in the gear chamber. Each compressormodule has an inlet shroud that is supported on an intermediatepartition of the compressor housing and a large plenum chamber isdefined in front of each compressor module in part by that intermediatepartition.

16 Claims, 13 Drawing Figures PATENTED APR 2 5 I972 SHEET 18F 6PATENTEUAFR 2 5 I972 SHEET 5 OF 6 QON @ON NON OON @Q VQ SHEET 8 OF 6 Tov RATENTEB APR 2 5 m2 COMPRESSOR SUMMARY OF INVENTION improvedmulti-stage centrifugal compressor arrangement employing a modulararrangement of impeller shafts having graduated rotational speeds so asto achieve advantageous compression conditions per compressor stage forthe several impellers while providing a convenient and economical drivearrangement.

A further object of the invention is to provide novel and improvedmulti-stage centrifugal compressor arrangement which has a compact flowpath arrangement through the impeller and cooler stages, requires asmall amount of space and presents an attractive appearance.

A further object of theinvention is to provide a novel and improvedmulti-stage centrifugal compressor arrangement having convenientlyarranged cooling and lubrication arrangements.

Still another object of the invention is to provide novel and improvedarrangements for driving a multi-stage centrifugal compressor assembly.

A further object of the invention is to provide a gaseous mediumcompressor arrangement having improved efficiency.

In accordance with one feature of the invention there is provided acentrifugal gaseous medium compressor system having a compressorhousing, with a plurality of compressor module support structures in thehousing which support a corresponding plurality of compressor moduleseach of which includes an impeller and bearing assembly. Partition meansin the housing divides the housing into a plurality of chambers with aninlet plenum chamber and a discharge chamber associated with eachcompressor module. The partition means further defines a flow pathbetween the discharge chamber of one compressor module and the inletplenum chamber of the next compressor module, and a cooler moduleincluding a series of heat exchanger surface elements is disposed inthat flow path. The housing has an outer wall with individual ports init through which the compressor and cooler modules may be withdrawn asindividual units.

In a preferred embodiment each compressor module includes a centrifugalcompressor impeller, a diffuser, and the necessary seals, bearings andpinion gear in a modular assembly, and each cooler module is aself-contained unit having heat exchanger surface elements and watermanifolds and the partition means. The system further includes a gearcasing that has a common wall with the compressor housing. A bull gearis mounted in that casing and the pinion gears of the compressor modulesextend through the common wall into the gear casing and are engaged bythe bull gear. A drive motor is disposed adjacent the gear casing andhas a motor shaft that extends into the gear casing and the bull gear ismounted directly on that motor shaft.

In accordance with another features of the invention there is providedcentrifugal gaseous medium compressor apparatus having a housing and acompressor assembly mounted within the housing. The compressor assemblyincludes an impeller assembly and an inlet shroud defining an inletpassage. A plenum chamber through which the gaseous medium to becompressed passes is immediately adjacent the compressor assembly inletshroud; the plenum chamber being within a distance equal to the inletdiameter of the inlet shroud from the forward blade edge of the impellerand having a cross-sectional area at least four times thecross-sectional inlet area of the compressor assembly as defined by itsinlet shroud. In preferred embodiments the cross-sectional area of theplenum chamber is'at least ten times the cross-sectional inlet area ofthe compressor assembly. This close coupled plenum chamber-compressorassembly arrangement provides a significant increase in compressorefficiency. Such arrangement also permits the close positioning of aninlet throttle valve without adversely affecting the performance of thecompressor.

In a particular embodiment, the compressor housing is a rectangularhousing in which three compressor modules and three cooler modules aremounted. This housing has dividing partitions which define the airpassages and close coupled plenum chambers that route the air in therequired sequence through the compressor and cooler modules. Thecompressor and cooler modules are assembled into the housing throughaccess ports in the front of the housing and are easily inspectable fromthese ports and easily removed without disconnecting drive structure orpiping. Water connections to the cooler modules are made on the backside of the compressor housing through appropriately sealed ferruleassemblies that facilitate insertion and removal.

The drive motor is of the face mounting configuration and an adapterplate bolted to the face of the motor serves as the rear wall of thegear casing. The hull gear is mounted directly on the drive motor shaft,thus eliminating the need for bull gear bearings and the problems ofcouplings and coupling misalignment. A common base for the compressorhousing and the drive motor contains a lubrication oil module andcontrol cabinet. The lubrication module is an assembly of the necessarylubrication oil conditioning equipment and typically includes alubrication oil cooler, a pump, pressure regulating valves andtemperature sensors.

Compressor controls include throttling means for throttling thecompressor inlet to maintain constant discharge pressure and also toprevent surge. Other controls include sensing, drive motor overloadprotection and lube oil temperature pressure sensing, cooling waterpressure and vibration sensors. Any one of the key elements of theassembly can be removed without disturbing other elements, including anyof the rotor assemblies, any of the coolers, the lubrication oil module,or the control module.

Other objects, features and advantages of the invention will be seen asthe following description of a particular embodiment progresses, inconjunction with the drawings, in which:

FIG. 1 is a perspective view of a three-stage centrifugal air compressorsystem constructed in accordance with the invention, showing acompressor module and a cooler module spaced from the compressorassembly housing;

FIG. 2 is a top plan view with parts broken away of the compressorsystem shown in FIG. 1;

FIG. 3 is side elevational view with parts broken away of the compressorsystem shown in FIG. 1;

FIG. 4a is a diagrammatic view of components of the compressor system;

FIG. 4b is an exploded diagrammatic view corresponding to FIG. 4a,showing the air flow path through components of the compressor system;

FIG. 5 is a sectional view showing details of a compressor moduleemployed in the system shown in FIG. 1;

FIG. 6 is a perspective view with parts broken away showing details of acooler module employed in the system shown in FIG. 1;

FIGS. 7-10 are sectional views taken along the lines 7-7,

8-8, 9-9, and 10-10, respectively, of FIG. 2; and

FIGS. 11 and 12 are sectional views taken along the lines 11-11 and12-12, respectively, of FIG. 3.

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to FIGS. 1-3, theapparatus includes a base 10 on which a compressor assembly housing 12is mounted at its left end and a prime mover 14 in the form of anelectric motor is mounted at its right end. A control panel 16 ismounted on one side of motor 14 and a system for supplying lubricatingoil to the compressor assembly is mounted on the opposite side of motor14. Chamber disposed between motor 14 and compressor housing 12 houses abull gear 22 that is mounted directly on the shaft 24 of motor 14.

The compressor assembly in housing 12 includes three compressor Stages30, 32 and 34 and three cooler structures 36, 38 and 40 disposed inrectangular housing 12. Each compressor stage and cooler structure isremovable as a unit through an access port in the left end wall 42 ofhousing 12, compressor stages 30, 32 and 34 being removable throughports 44, 46 and 48 covered by plates 50, 52 and 54, respectively; andcooler stages 36, 38 and 40 being removable through ports 56, 58, 60 andhaving integral cover plates 62, 64 and 66, respectively. Inlet conduit68 is attached to plate 50 and may include a throttling valve; andoutlet conduit 70 extends upwardly from the top wall 72 of housing 12.

A diagrammatic view of the compressor assembly is shown in FIG. 4a and acorresponding exploded view is shown in FIG. 4b. Air is introduced intothe compressor assembly through inlet conduit 68 to plenum chamber 74which communicates with the inlet of first compressor stage 30. Thatcompressor stage discharges air into discharge chamber 76 whichtranslates the compressed air through cooler 36 to plenum chamber 78 atthe inlet to compressor stage 32. The compressed air from that stage isdischarged into chamber 80 for transfer to cooler 38 to plenum chamber82 which communicates with the inlet to compressor stage 34. Compressorstage 34 is mounted to discharge air into discharge chamber 84 andtransfer that air through aftercooler 40 and chamber 86 to outletconduit 70.

A sectional view of compressor module stage 30 and plenum chamber 74which is illustrative of the construction of module stages 32 and 34(although those stages are of graduated smaller size) and theirassociated plenum chambers, is shown in FIG. 5.

The compressor module is received directly in a mounting boss 90 thatprojects forwardly from the front wall 92 of the gear case 20 andreceives its primary support from this mounting structure. Additionalsupport is provided by the interconnection of the inlet shroud 94 of themodule with partition 96 in the compressor case between chambers 74 and76. The compressor impeller 98 and shaft 100 are an integral assembly,the impeller 98 being cast from a corrosion resistant steel and weldedto shaft 100. The pinion gear 102 is press fitted on shaft 100. Shafthousing 104 includes hydrodynamic radial bearings 106, 108, the impellerend bearing 106 of the three lobed type and the pinion end bearing 108is of the simple journal type. Thrust bearing 110 is of the simplestepped type. The main thrust is towards the impeller and a thrustwasher I12 captured by the pinion 102 provides the main positioningsurface. A position control thrust bearing 114 located at the end of thebearing housing 104 uses the back face of the pinion as a runnersurface. The shaft seal 116 is a two-stage seal, the primary seal or oilside being a mechanical or nose type seal and the second stage a simplelabyrinth. The oil to the radial and thrust bearings is supplied fromthe lubrication supply line 118 into the compressor cartridge via anannular passage 120 formed by the stepped diameter of the bearinghousing 104 and the receiving bore in the support boss 90. Lubricationflow control is established by the sizing of the drilled holes requiredto port the oil to various bearing supply areas. Passage 122 provides avent. Drainage from the bearings is ported away from the bull gear andflows to an annular recess 124 covered by plate 126 in the forward faceof the bull gear chamber 20.

The compressor diffuser 128 is formed by a flat plate having a series ofvanes 130 cast thereon. This plate is bolted to the housing 104 and theshroud 94 is secured in accurately centered relation to the diffuser 128and bearing cartridge 104 by dowel pins and bolts. The entire compressormodule may be removed as a unit by unbolting the inlet bellmouth shroudstructure 94 from partition 96 and sliding the unit out to initiallydisengage pinion 102 from bull gear 22 and then to remove the unitthrough the plenum chamber 74 and port 44.

Plenum chamber 74 is close coupled to compressor module 30, wall 96being a partition separating plenum chamber 74 from compressor dischargechamber 76. The plenum chamber side of wall 96 is located at a distancefrom the front end 132 of impeller blades 134 of about one-half thecompressor inlet diameter indicated by dimension 136 and chamber 74 hasa cross-sectional area about 25 times the cross-sectional area of thecompressor inlet and a length of about twice the inlet diameter 136.

A diagrammatic view of a cooler module is shown in FIG. 6. In a typicalmodule, the intercooler includes a multipass, cross-counterflowarrangement having tube-fin heat exchange surfaces. The air side isformed of aluminum plates 140 spaced approximately 0.050 inch apart andthe water side formed by inch copper tubing 142. Each intercooler modulehas two headers 144, 146, both headers having baffling 148 to providethe appropriate number of water passes. The inner header 146 containinginlet and discharge ports I50, 152. The flow is from header section146-1 through tubes 142 to header section 144-1 and return through asecond set of tubes 142 to header section 1462 and then return again toheader section 144-2 for final pass back through still another set oftubes 142 to header section 146-3 and discharge through connection 152.These ports match up with appropriate water supply and drain portstructures 154, 156 in wall 92 of the compressor case and the interfacejunction is sealed by O-ring seal ferrules 158. Moisture condensed outduring the intercooling process is collected by the fins 140 and drainedto the bottom of the intercooler chamber chamber 160 and to a sump 162(FIG. 8) which is piped through usual water traps to an overboard drain.Flexible seal structures 164 are mounted on either side of the coolermodule and engage two opposed walls 166, 168 of the chamber 160 in whichthe module is received. At the front end of the cooler module is aflange structure which is bolted with appropriate seals to the wall 42of the compressor assembly housing 12, securing the module in positionin the flow path in the compressor system. The entire cooler module maybe removed as a unit by unbolting the plate structure and sliding theunit out to remove the unit through the port.

Further details of the assembly are indicated in FIGS. 7-12. An end viewof the compressor assembly in FIG. 7 shows the access plates over theaccess ports in wall 42. In FIG. 8 there are indicated the cooling waterinlet line 200 and cooling water outlet line 202 that communicate witheach of the three cooler modules, lubrication supply line 204 whichcommunicates with supply manifold 122 and lubrication drain line 206which communicates with annular drain manifold 124. This manifold, asindicated in FIGS. 5 and 8, may be machined directly in the wall 92.With reference to FIGS. 9-12, plenum chamber 74 is defined by partitions210,212, 214, top wall 72, transverse wall 96 and front wall 42.Discharge chamber 76 is defined by rearward extension of wall 210, sidewall 218, top wall 216, lower wall 220, partition walls 96, 212 and 214,and wall 92 between the compressor compartment and the bull gearcompartment. Thus discharge chamber 76 has common walls with plenumchamber 74. Intercooler module 36 is disposed in a chamber whose upperwall is an extension of partition 214 and lower wall is a portion of thedrain floor wall 220, the inner side wall is partition 222; and frontand rear walls are structures 42 and 92, respectively.

The plenum chamber 78 has as a top wall a portion of partition 214, abottom wall part of partition 220, a side wall as partition 224, frontwall 42 and rear wall 96. The discharge chamber 80 for compressor module32 is defined by partitions 214, 220, 222, 224, front wall 42 and rearwall 92. intercooler 38 is disposed between the discharge chamber 80 andinlet plenum chamber 82 to the third compressor module. Chamber 82 isbounded by side wall 226, partitions 96 and 214, top wall 216, and frontwall 42. The discharge chamber 84 for the third stage is formed betweenpartition 230 and top wall 216, partition 210 and side wall 226, andpartition 96 and rear wall 92. Aftercooler 40 is disposed in thischamber and the air after flowing through that aftercooler is dischargedto conduit 70.

As an illustrative example, in this compressor assembly with an 800horsepower motor, compressor stage 30 has a shaft speed of 61,800 rpm,compressor stage 32 has a shaft speed of 42, 400 rpm, and compressorstage 34 has a shaft speed of 29,100 rpm. A compressor unit of thisframe size has an overall width of 4 feet and an overall height of 5feet and is 6 feet, 9 inches long.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention as defined in the claims.

What is claimed is:

1. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a housing outer wall structure opposite to and spacedfrom said common wall, said outer wall structure having a plurality ofports therein aligned with corresponding ones of said compressor modulesupport structures, and a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear, each saidcompressor module being removable as a unit from its support structurethrough the corresponding port in said outer wall structure of saidhousing.

2. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear, and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units, and a cooler module disposed in said housing in a flowpath between the discharge chamber of one compressor module and theplenum chamber of another compressor module, said cooler moduleincluding a series of heat exchanger surface elements, and said outerwall further including a port through which said cooler module may bewithdrawn from said housing as a unit.

3. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units, said partitioning means cooperating with each saidinlet shroud to define a plurality of plenum chambers between said inletshroud and said outer wall, and each said plenum chamber beingassociated with a corresponding compressor module and having across-sectional area at least four times the cross-sectional area of thecompressor module inlet passage as defined by said inlet shroud.

4. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhosuing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units and an annular drain channel formed in said common walland communicating via said module support structures with said shaft andbearing assemblies.

5. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a

corresponding plurality of compressor modules supported in said modulesupport structures, each said compressor module including a shaft andbearing assembly, an impeller, a pinion gear, a diffuser structure andan inlet shroud supported on said shaft and bearing assembly, each saidinlet shroud being supported on an intermediate partition of saidhousing and each said pinion gear being disposed in said gear casing fordriving by said bull gear and an outer wall of said housing oppositesaid common wall having corresponding ports through which saidcompressor modules may be removed from said housing as units and a drivemotor disposed adjacent said gear casing, said drive motor having amotor shaft extending into said gear casing and said bull gear beingmounted directly on said motor shaft.

6. The system as claimed in claim 5 wherein each said plenum chamber hasa cross-sectional area at least four times the cross-sectional area ofthe compressor module inlet passage as defined by said inlet shroud.

7. The system as claimed in claim 6 wherein said partitioning meanscooperates with each said inlet shroud to define a plenum chamberbetween said inlet shroud and said outer wall.

8. The system as claimed in claim 7 and further including a coolermodule disposed in said housing in a flow path between the dischargechamber of one compressor module and the plenum chamber of anothercompressor module, said cooler module including a series of heatexchanger surface elements, and said outer wall further including a portthrough which said cooler module may be withdrawn from said housing as aunit.

9. The system as claimed in claim 8 and further including an annulardrain channel formed in said common wall and communicating via saidmodule support structures with said shaft and bearing assemblies.

10. A centrifugal gaseous medium compressor system comprising acompressor housing, a plurality of compressor module support structuresin said housing, a corresponding plurality of compressor modulessupported in said module support structures, partition means in saidhousing dividing said housing into a plurality of chambers with an inletplenum chamber and a discharge chamber associated with each compressormodule, said partition means further defining a flow path between thedischarge chamber of one compressor module and the inlet plenum chamberof another compressor module, a cooler module support structure disposedin said flow path, a cooler module including a series of heat exchangersurface elements releasably secured to said cooler module supportstructure, said housing having an outer wall with individual spacedports therein and aligned with corresponding ones of said compressormodule support structures and said cooler module support structurethrough which said compressor and coller modules may be withdrawn asindividual units and means for sealing said ports.

11. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into two chambers,an aperture in said partitioning means, a gear casing having a commonwall with said compressor housing, a bull gear mounted for rotation insaid gear casing, a compressor module support structure on said commonwall and extending into one of said chambers, a housing outer wall onthe opposite side of said chambers from said common wall, said outerwall having a port therein aligned with said compressor module supportstructure, a compressor module supported in said module supportstructure, said compressor module including shaft and bearing assembly,an impeller, a pinion gear, a diffuser structure and an inlet shroudsupported on said shaft and bearing assembly, said inlet shroud beingsecured in sealing relation in said aperture of said partitioning means,the second of said chambers being a plenum chamber through which themedium to be compressed is supplied and having a cross-sectional area atleast four times the cross-sectional area of the compressor module inletpassage as defined by said inlet shroud, and said shaft and bearingassembly extending through said common wall so that said pinion gear isdisposed in said gear casing for driving by said bull gear, saidcompressor module being removable as a unit from its support structurethrough said port in said outer wall of said housing.

12. Centrifugal gaseous medium compressor apparatus comprising ahousing, a compressor assembly mounted within the housing, saidcompressor assembly including an impeller assembly and an inlet shroudthat defines an inlet passage to said impeller assembly, structuredefining a plenum chamber through which the gaseous medium to becompressed passes immediately adjacent the compressor assembly inletshroud, said plenum chamber being within a distance equal to the inletdiameter of said inlet shroud from the forward blade edge of saidimpeller assembly and having a cross-sectional area at least four timesthe cross-sectional inlet area of said compressor assembly as defined bysaid inlet shroud.

13. The compressor assembly as claimed in claim 12 wherein thecross-sectional area of said plenum chamber is at least ten times saidcross-sectional inlet area of said compressor assembly.

14. The apparatus as claimed in claim 13 wherein said apparatus includesa plurality of compressor assembly modules and associated close coupledplenum chambers and further including a cooler module disposed in saidhousing in a flow path between the discharge chamber of one compressormodule and the plenum chamber of another compressor module, said coolermodule including a series of heat exchanger surface elements, and saidhousing further including a port through which said cooler module may bewithdrawn from said housing as a unit.

15. The apparatus as claimed in claim 14 and further includingpartitioning means cooperating with each said inlet shroud to define aplenum chamber between said inlet shroud and the outer wall of saidhousing.

16. The apparatus as claimed in claim 15 and further including a drivemotor having a motor shaft, and a bull gear mounted directly on saidmotor shaft for engaging drive pinions of said compressor assemblynlodules.

1. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a housing outer wall structure opposite to and spacedfrom said common wall, said outer wall structure having a plurality ofports therein aligned with corresponding ones of said compressor modulesupport structures, and a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear, each saidcompressor module being removable as a unit from its support structurethrough the corresponding port in said outer wall structure of saidhousing.
 2. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhousiNg, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear, and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units, and a cooler module disposed in said housing in a flowpath between the discharge chamber of one compressor module and theplenum chamber of another compressor module, said cooler moduleincluding a series of heat exchanger surface elements, and said outerwall further including a port through which said cooler module may bewithdrawn from said housing as a unit.
 3. A centrifugal gaseous mediumcompressor system comprising a compressor housing, means partitioningsaid housing into a plurality of chambers, a gear casing having a commonwall with said compressor housing, a bull gear mounted for rotation insaid gear casing, a plurality of compressor module support structuresmounted directly on said common wall, a corresponding plurality ofcompressor modules supported in said module support structures, eachsaid compressor module including a shaft and bearing assembly, animpeller, a pinion gear, a diffuser structure and an inlet shroudsupported on said shaft and bearing assembly, each said inlet shroudbeing supported on an intermediate partition of said housing and eachsaid pinion gear being disposed in said gear casing for driving by saidbull gear and an outer wall of said housing opposite said common wallhaving corresponding ports through which said compressor modules may beremoved from said housing as units, said partitioning means cooperatingwith each said inlet shroud to define a plurality of plenum chambersbetween said inlet shroud and said outer wall, and each said plenumchamber being associated with a corresponding compressor module andhaving a cross-sectional area at least four times the cross-sectionalarea of the compressor module inlet passage as defined by said inletshroud.
 4. A centrifugal gaseous medium compressor system comprising acompressor housing, means partitioning said housing into a plurality ofchambers, a gear casing having a common wall with said compressorhosuing, a bull gear mounted for rotation in said gear casing, aplurality of compressor module support structures mounted directly onsaid common wall, a corresponding plurality of compressor modulessupported in said module support structures, each said compressor moduleincluding a shaft and bearing assembly, an impeller, a pinion gear, adiffuser structure and an inlet shroud supported on said shaft andbearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units and an annular drain channel formed in said common walland communicating via said module support structures with said shaft andbearing assemblies.
 5. A centrifugal gaseous medium compressor systemcomprising a compressor housing, means partitioning said housing into aplurality of chambers, a gear casing having a common wall with saidcompressor housing, a bull gear mounted for rotation in said gearcasing, a plurality of compressor module support structures mounteddirectly on said common wall, a corresponding plurality of compressormodules supported in said module suppOrt structures, each saidcompressor module including a shaft and bearing assembly, an impeller, apinion gear, a diffuser structure and an inlet shroud supported on saidshaft and bearing assembly, each said inlet shroud being supported on anintermediate partition of said housing and each said pinion gear beingdisposed in said gear casing for driving by said bull gear and an outerwall of said housing opposite said common wall having correspondingports through which said compressor modules may be removed from saidhousing as units and a drive motor disposed adjacent said gear casing,said drive motor having a motor shaft extending into said gear casingand said bull gear being mounted directly on said motor shaft.
 6. Thesystem as claimed in claim 5 wherein each said plenum chamber has across-sectional area at least four times the cross-sectional area of thecompressor module inlet passage as defined by said inlet shroud.
 7. Thesystem as claimed in claim 6 wherein said partitioning means cooperateswith each said inlet shroud to define a plenum chamber between saidinlet shroud and said outer wall.
 8. The system as claimed in claim 7and further including a cooler module disposed in said housing in a flowpath between the discharge chamber of one compressor module and theplenum chamber of another compressor module, said cooler moduleincluding a series of heat exchanger surface elements, and said outerwall further including a port through which said cooler module may bewithdrawn from said housing as a unit.
 9. The system as claimed in claim8 and further including an annular drain channel formed in said commonwall and communicating via said module support structures with saidshaft and bearing assemblies.
 10. A centrifugal gaseous mediumcompressor system comprising a compressor housing, a plurality ofcompressor module support structures in said housing, a correspondingplurality of compressor modules supported in said module supportstructures, partition means in said housing dividing said housing into aplurality of chambers with an inlet plenum chamber and a dischargechamber associated with each compressor module, said partition meansfurther defining a flow path between the discharge chamber of onecompressor module and the inlet plenum chamber of another compressormodule, a cooler module support structure disposed in said flow path, acooler module including a series of heat exchanger surface elementsreleasably secured to said cooler module support structure, said housinghaving an outer wall with individual spaced ports therein and alignedwith corresponding ones of said compressor module support structures andsaid cooler module support structure through which said compressor andcoller modules may be withdrawn as individual units and means forsealing said ports.
 11. A centrifugal gaseous medium compressor systemcomprising a compressor housing, means partitioning said housing intotwo chambers, an aperture in said partitioning means, a gear casinghaving a common wall with said compressor housing, a bull gear mountedfor rotation in said gear casing, a compressor module support structureon said common wall and extending into one of said chambers, a housingouter wall on the opposite side of said chambers from said common wall,said outer wall having a port therein aligned with said compressormodule support structure, a compressor module supported in said modulesupport structure, said compressor module including shaft and bearingassembly, an impeller, a pinion gear, a diffuser structure and an inletshroud supported on said shaft and bearing assembly, said inlet shroudbeing secured in sealing relation in said aperture of said partitioningmeans, the second of said chambers being a plenum chamber through whichthe medium to be compressed is supplied and having a cross-sectionalarea at least four times the cross-sectional area of the compressormodule inlet passage as defined by said inlet shroud, and said shaft andbearing assemblY extending through said common wall so that said piniongear is disposed in said gear casing for driving by said bull gear, saidcompressor module being removable as a unit from its support structurethrough said port in said outer wall of said housing.
 12. Centrifugalgaseous medium compressor apparatus comprising a housing, a compressorassembly mounted within the housing, said compressor assembly includingan impeller assembly and an inlet shroud that defines an inlet passageto said impeller assembly, structure defining a plenum chamber throughwhich the gaseous medium to be compressed passes immediately adjacentthe compressor assembly inlet shroud, said plenum chamber being within adistance equal to the inlet diameter of said inlet shroud from theforward blade edge of said impeller assembly and having across-sectional area at least four times the cross-sectional inlet areaof said compressor assembly as defined by said inlet shroud.
 13. Thecompressor assembly as claimed in claim 12 wherein the cross-sectionalarea of said plenum chamber is at least ten times said cross-sectionalinlet area of said compressor assembly.
 14. The apparatus as claimed inclaim 13 wherein said apparatus includes a plurality of compressorassembly modules and associated close coupled plenum chambers andfurther including a cooler module disposed in said housing in a flowpath between the discharge chamber of one compressor module and theplenum chamber of another compressor module, said cooler moduleincluding a series of heat exchanger surface elements, and said housingfurther including a port through which said cooler module may bewithdrawn from said housing as a unit.
 15. The apparatus as claimed inclaim 14 and further including partitioning means cooperating with eachsaid inlet shroud to define a plenum chamber between said inlet shroudand the outer wall of said housing.
 16. The apparatus as claimed inclaim 15 and further including a drive motor having a motor shaft, and abull gear mounted directly on said motor shaft for engaging drivepinions of said compressor assembly modules.